Environment-responsive method for maintaining an electronic device

ABSTRACT

A method of indicating operational status of an electronic device, the device providing an indication of device operational status as a result of a self-test, the method including the following steps: monitoring an environmental condition; changing an indication of device operational status from a first indication to a second indication if the monitored environmental condition changes from a first condition to a second condition, this changing step being performed without performing a self-test. In certain embodiments, the monitored environmental condition is a monitored temperature, the first condition is a first temperature and the second condition is a second temperature. The electronic device may be battery-operated, in which case the self-test is a battery capacity test. In these embodiments, the method also may include the step of performing the battery capacity test when the monitored temperature reaches the second temperature if there is no indication of device operational status corresponding to the second temperature stored in memory, the second temperature is lower than a temperature associated with an indication of a non-waning device operational status stored in memory, and the second temperature is higher than a temperature associated with an indication of a warning operational status; and indicating device operational status as a result of the battery capacity test. The method may also include the step of storing in memory an association between the second temperature and device operational status.

RELATED APPLICATION

This application is a divisional of application Ser. No. 08/911,710filed Aug. 15, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to electronic devices andenvironment-dependent methods of maintaining the devices and indicatingoperational status of the devices. In particular, this invention relatesto temperature-dependent methods of maintaining battery-operatedexternal defibrillators and indicating their operational status.

2. Description of the Prior Art

Electronic devices that are infrequently used may be designed to performautomatic self-tests on a preset schedule, in response to an event orcondition, or otherwise and to indicate the results of those self-teststo a potential user. An example can be found in certain externaldefibrillators that automatically self-test battery capacity and otherdefibrillator functions and components and indicate the results of thoseself-tests (i.e., the device's operational status) through visualdisplays and/or audible tones.

U.S. patent application Ser. No. 08/240,272 describes a battery-operatedautomatic external defibrillator (AED) designed for infrequent use. Thedevice described in that patent application performs a variety of daily,weekly and monthly self-tests while in stand-by mode (i.e., when notpowered-on to treat a patient, to review past treatment events, etc.)and indicates the operational status of the device using an "OK" or "NotOK" fail-safe visual display and using an audible tone generator. One ofthe device parameters monitored during the self-tests is remainingbattery capacity.

The '272 application also suggests performing a group of self-testsautomatically in response to exposure of the defibrillator totemperature extremes, although the exact nature of theenvironmentally-triggered self-tests is not disclosed. The disclosure ofthe '272 application is incorporated herein by reference.

There are many other types of battery-operated devices as well. Somebattery-operated devices automatically track remaining battery capacityand indicate device status or make some other change based, at least inpart, on remaining battery capacity. See, e.g., U.S. Pat. No. 3,895,284;U.S. Pat. No. 4,207,514; U.S. Pat. No. 4,525,055; U.S. Pat. No.4,693,119; U.S. Pat. No. 4,725,784; U.S. Pat. No. 4,931,737; U.S. Pat.No. 5,065,084; U.S. Pat. No. 5,130,659; U.S. Pat. No. 5,162,741; andU.S. Pat. No. 5,483,165. The disclosures of these patents areincorporated herein by reference.

For example, Bates U.S. Pat. No. 5,162,741 describes a battery monitorthat continuously samples the battery load current and temperature. Thedevice continuously displays remaining battery capacity based on atemperature-compensated measurement of the amount of current drawn fromthe battery.

Hishiki U.S. Pat. No. 4,931,737 describes a battery capacity measurementcircuit using a capacitor having thermal and age-variationcharacteristics to compensate for the thermal and age-variationcharacteristics of the battery. Specifically, the capacitor'scapacitance, like the battery capacity, is maximum at room temperatureand decreases with either an increase or decrease in ambienttemperature. The capacitor is used to generate a pulse signal whosefrequency varies with temperature as the capacitance (and therefore thebattery capacity) changes, with the frequency being lowest at roomtemperature and increasing with an increase or decrease in ambienttemperature. The pulse signals are counted by a counter to computebattery discharge and, thereby, remaining battery capacity.

Landau et al. U.S. Pat. No. 5,454,710 describes a battery monitoring anddisplay system which adjusts actual measurements of remaining batterycapacity by fixed percentages when the ambient temperature is in certaindefined ranges.

SUMMARY OF THE INVENTION

An indication of device operating status can be critically important forcertain electronic devices. For example, external defibrillators areused to treat victims of sudden cardiac arrest through the delivery ofan electric shock. Time is of the essence in getting this defibrillationtherapy to the victim. In fact, the patient's chances of survival arereduced by about 10% for each minute that therapy is withheld. If adefibrillator incorrectly reports its operational status, valuable timecan be lost in determining the cause of the error and remedying theproblem. A defibrillator's operational status indicator must thereforebe extremely reliable in its indication of device status.

Environmental conditions can materially affect the operational status ofan electronic device (such as a defibrillator). In particular, high and,especially, low temperatures can have a dramatic affect on availablebattery capacity. It is therefore an object of this invention to takeambient environmental conditions into account when indicatingoperational status of an electronic device, making that statusindication more responsive to environmental changes, and therebyimproving the reliability of that status indication.

Self-testing itself can materially affect the operational status of anelectronic device by, for instance, depleting resources such as batterypower. It is therefore another object of this invention to change, undercertain environmental conditions, the indication of device operationalstatus based on historical self-test results without actually performinga new self-test.

The invention is a method of indicating operational status of anelectronic device (such as an external defibrillator), the deviceproviding an indication of device operational status as a result of aself-test, the method including the following steps: monitoring anenvironmental condition (such as temperature); changing an indication ofdevice operational status from a first indication to a second indicationif the monitored environmental condition changes from a first conditionto a second condition, this changing step being performed withoutperforming a self-test. The first indication may be a non-warningindication and the second indication may be a warning indication. In oneembodiment, the second condition is a target condition, and the methodfurther includes the step of setting a new target condition.

In certain embodiments, the monitored environmental condition is amonitored temperature, the first condition is a first temperature andthe second condition is a second temperature. The electronic device maybe battery-operated, in which case the self-test is a battery capacitytest. In these embodiments, the method also may include the step ofperforming the battery capacity test when the monitored temperaturereaches the second temperature if there is no indication of deviceoperational status corresponding to the second temperature stored inmemory, the second temperature is lower than a temperature associatedwith an indication of a non-warning device operational status stored inmemory, and the second temperature is higher than a temperatureassociated with an indication of a warning operational status; andindicating device operational status as a result of the battery capacitytest. The method may also include the step of storing in memory anassociation between the second temperature and device operationalstatus.

In other embodiments, the method includes, without performing aself-test, the step of changing the indication of device operationalstatus from the second indication to the first indication if themonitored environmental condition reaches the first condition. Themethod may also include the step of retrieving from memory the secondindication of device operational status, the second indication of deviceoperational status being associated with the second condition. In suchcase, the method may include, following the retrieving step but prior tothe changing step, the step of determining whether the second indicationof device operational status is valid, the changing step being performedonly if the second indication of device operational status is valid. Themethod may also include the step of performing a self-test if the secondindication of device operational status is invalid.

In still other embodiments, the method includes the steps of performingan automatic self-test when the monitored environmental conditionreaches the second condition if there is no indication of deviceoperational status corresponding to the second condition stored inmemory; and indicating device operational status as a result of theself-test. The method may also include storing in memory an associationbetween the second condition and device operational status.

In another embodiment, the invention is a method of indicatingoperational status of a battery-operated, automatically self-testingdevice (such as an external defibrillator), the device providing anindication of device operational status as a result of a self-test, andincludes the following steps: monitoring a temperature; if the monitoredtemperature reaches a target temperature, retrieving from memoryassociations between temperature and indications of device operationalstatus; if the highest temperature associated with an indication of awarning device operational status is higher than the lowest temperatureassociated with an indication of a non-warning device operationalstatus, performing an automatic battery capacity test and indicatingdevice operational status as a result of the battery capacity test. Inone embodiment, the method includes the step of storing in memory anassociation between the target temperature and an indication of deviceoperational status.

In yet another embodiment, the invention is a method of indicatingoperational status of an electronic device (such as an externaldefibrillator), including the following steps: monitoring anenvironmental condition (such as temperature); performing a plurality ofself-tests (such as battery capacity tests) at a plurality ofenvironmental conditions to determine as self-test results whetherdevice operational status is acceptable or unacceptable at eachenvironmental condition; storing an association of self-test results andenvironmental conditions at which the self-tests were performed; andindicating operational status of the electronic device based on theself-test results. In one embodiment, the method includes the step ofstoring a maximum number of self-test results.

In one particular embodiment the environmental condition is temperatureand the self-test is a battery-capacity test, and the method includesthe following steps: if a battery capacity test has not been performedat a target temperature, and if the target temperature is lower than thetemperature of the lowest acceptable battery capacity test result andhigher than the temperature of the highest unacceptable battery capacitytest result: performing a battery capacity test;

storing an association of a battery capacity test result from theprevious step and the target temperature; indicating the batterycapacity test result stored in the previous step; and

setting a new target temperature.

The method may also include, if a temperature of an unacceptable batterycapacity test result is higher than a temperature of an acceptablebattery capacity test result, the steps of:

performing a battery capacity test; storing an association of a batterycapacity test result from the previous step and temperature; andindicating the battery capacity test result stored in the previous step.In this embodiment, the method may also include, if the device batterycapacity has been tested at the target temperature, the step ofindicating the stored battery capacity test result associated with thetarget temperature.

The invention will be described in more detail below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a defibrillator which can be used to implementthe methods of this invention.

FIG. 2 is a flowchart showing one preferred method of indicating theoperational status of a battery-operated, automatically self-testingdevice.

FIG. 3 is a flowchart showing another embodiment of the methods of thisinvention.

FIG. 4 is a flowchart showing yet another embodiment of this invention.

FIG. 5 is a block diagram showing an external defibrillator that may beused to implement the methods of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As discussed above, environmental changes can affect the results of abattery self-test and potentially other self-tests as well. It is notalways necessary, and sometimes undesirable, to run a self-test,however. One aspect of this invention, therefore, is a method ofindicating the operational status (e.g., through a "warning" indication)of an electronic, self-testing device based on recent historicalself-test results, without actually performing a new self-test, such asa battery capacity test. This aspect of the invention is illustratedwith reference to the battery-operated external defibrillator shown inFIG. 1. It should be understood that this aspect of the invention isapplicable to other battery-operated and non-battery-operated electronicdevices as well.

In FIG. 1, external defibrillator 10 includes a high voltage deliverysystem 14 operating under the control of controller 12 to deliver anelectric shock to an electrode interface 16. The high voltage deliverysystem may include a power transformer, switches and other circuitelements known in the defibrillator art. Power for operating thedefibrillator and for the electrical shock comes from battery 24.

In the preferred embodiment, defibrillator 10 automatically performsself-tests under the control of a self-test system 18 and indicates itsoperational status on a status indicator 22. The self-tests may includea battery capacity test and tests of other defibrillator systems orcomponents. Status indicator 22 may be any object which informs the userof device status through visual, audible, tactile, or other sensorymeans (e.g., a light, a text display, an electrically or mechanicallyaltered symbol, a beeper, or a spoken word generator). The self-testsystem may be an integral part of the controller 12, of course, withoutdeparting from the scope of this invention.

Details of a defibrillator self-test system (including a batterycapacity test) may be found in U.S. patent application Ser. No.08/240,272, the disclosure of which is incorporated herein by reference.Details of a preferred battery capacity test may be found in U.S. Pat.No. 5,483,165, which is also incorporated herein by reference. The exactnature and design of the battery capacity test and other self-tests formno part of this invention.

Defibrillator 10 has a environmental sensor 20 which can be used todetermine whether an environmental condition (such as temperature,humidity, chemical concentration, radiation level, altitude, mechanicalshock or vibrations, etc.) is within the defibrillator's specifiedoperating range and whether that environmental condition has exceededsome predefined limit. Controller 12 may also use sensor 20 to identifywarning states or other device operational status and to indicate devicestatus on status indicator 22 in response to a change in theenvironmental condition (whether or not the defibrillator is within itsspecified operating range) without performing a battery capacity test orother self-test.

External defibrillator 10 has at least three operational modes. In usemode, a controller 12 operates a high-voltage delivery system 14 todeliver an electrical shock to a patient through an electrode interface16. In self-test mode, controller 12 automatically tests one or more ofthe defibrillator's circuits or functions (such as the defibrillator'sbattery) in response, for example, to a request for a self-test from aself-test initialization generator 18 and/or an environmental sensor 20and indicates defibrillator operating status on a status indicator 22.More details about automatic self-tests in external defibrillators maybe found in the '272 patent application. The exact nature of theself-tests is not a part of this invention, except as indicated herein.

Finally, in stand-by mode, controller 12 conserves power by simplymonitoring temperature and other self-test initialization criteria (suchas elapsed or real time) and by watching for a request to use thedefibrillator, in which cases the defibrillator will move out ofstand-by mode to self-test mode or use mode, respectively. Power for theelectric shock and for operating the defibrillator is supplied bybattery 24.

In one embodiment of the invention, defibrillator 10 stores in memory 21associations between environmental conditions and device operationalstatus indications. For example, warning indications may be stored inassociation with particular temperatures or temperature ranges, andnon-warning indications may be stored in association with othertemperatures or temperature ranges. In some cases, defibrillator 10 usesthese stored associations between environmental conditions and devicestatus indications to indicate warnings, or to remove warningindications, in response to environmental changes monitored by sensor 20without actually performing new battery capacity tests or otherself-tests.

One preferred method of indicating the operational status of anelectronic, self-testing device is shown in the flowchart of FIG. 2. Anenvironmental condition (such as temperature, humidity, etc.) ismonitored (block 200) to determine whether a predetermined target hasbeen reached (block 202). If so, the device retrieves from memory anydevice operational status that may be stored in association with thetarget (block 204). At block 206, the device uses the stored statusinformation to indicate device status on a device status indicator (suchas status indicator 22 of the defibrillator shown in FIG. 1). At block208, the device sets the next target that will trigger the retrieval ofdevice status information from memory and continues to monitor theenvironmental condition. In this way, the device is able to indicatechanges in device operational status based on historical self-testresults without actually performing a new battery capacity test or otherself-test.

FIG. 3 is a flowchart showing another embodiment of the invention. Inthis embodiment, the environmental condition is temperature, which ismonitored (block 300) to determine whether a predetermined temperaturetarget has been reached (block 302). If there is a device operationalstatus stored in device memory in association with the targettemperature, the associated device operational status is retrieved frommemory (block 306) and indicated via the device status indicator (block308). If, however, there is no device operational status informationstored in association with the target temperature, the device performs abattery capacity test or other self-test (block 312), stores in devicememory an indication of device status in association with the targettemperature (block 314) and indicates the newly-determined device status(block 308). A new temperature target is then set (block 310), and thedevice continues to monitor temperature.

FIG. 4 is a flowchart showing yet another embodiment of this invention.This embodiment is based on the assumption that available batterycapacity always decreases with a decline in temperature. As in theflowchart of FIG. 3, the device monitors temperature (block 400) andlooks to see whether a temperature target has been reached (block 402).If so, the device determines whether there are valid temperature/statusassociations stored in memory (block 403). Stored associations may beinvalid for many reasons, including age of the stored associations,recent use history of the device, etc. In a preferred embodiment, thedevice determines the validity of stored associations by determiningwhether the highest temperature stored in association with an indicationof a warning device operational status is higher than the lowesttemperature stored in association with an indication of a non-warningdevice operational status. The age of the stored associations are keptwithin 14 days by using only the last 14 associations stored, since theself-tests on which the associations are based are performed at afrequency no greater than once per day and since any postponement of aself-test invalidates the stored associations.

If the associations are valid, the device retrieves the associateddevice status from memory (block 406), indicates that status on thedevice status indicator (block 408), and sets the next temperaturetarget (block 410). If, on the other hand, the stored temperature/statusassociations are not valid, the device ignores the storedtemperature/status association and performs a battery capacity test(block 416) before indicating device status (block 408) and setting thenext temperature target.

If there is no device operational status information stored inassociation with the target temperature, the device determines whetherthe target temperature is less than the lowest temperature stored inassociation with a non-warning (i.e., acceptable) device operationalstatus (block 412). If not (i.e., if the target temperature is higherthan a known non-warning temperature), based on the assumption thatbattery capacity increases with increasing temperature, the deviceindicates a non-warning status without performing a battery capacitytest (block 420).

If the target temperature is less than the lowest temperature stored inassociation with a non-warning status but not greater than the highesttemperature stored in association with a warning (i.e., unacceptable)device operational status (i.e., if the target temperature is coolerthan a known warning temperature), the device indicates a warning statuswithout performing a battery capacity test (block 422) based on theassumption that battery capacity decreases with a decrease intemperature.

It should be understood that, for purposes of this invention, the targettemperatures may be temperature regions and not precise temperatures.

The following is a specific example of the methods of this invention asimplemented in an external defibrillator such as defibrillator 10 inFIG. 1. In this example, the specified operating range for defibrillator10 is 0° C. to 50° C. with the measurement accuracy being ±2.5° C.Defibrillator 10 maintains in device memory 21 a Recent TemperatureHistory List (RTHL) containing the temperature reading and battery testresults (e.g., "good battery" or "not good battery"; "warning" or "nowarning"; etc.) for up to the most recent 14 battery capacity tests. Thepotential temperature measurements over the defibrillator's operatingrange are divided into bins as follows:

    ______________________________________                                        Temperature Range                                                                            Classification Bin #                                           ______________________________________                                        >52.5 C.       8                                                               30.0 to 52.5! C.                                                                            7                                                               20.0 to 30.0) C.                                                                            6                                                               12.5 to 20.0) C.                                                                            5                                                               7.5 to 12.5) C.                                                                             4                                                               2.5 to 7.5) C.                                                                              3                                                               -2.5 to 2.5) C.                                                                             2                                                               -7.5 to -2.5) C.                                                                            1                                                              <-7.5 C.       0                                                              ______________________________________                                    

Temperature/status associations in the RTHL are invalidated whenever thedefibrillator is actually used (i.e., when the device is placed in "use"mode) or when a battery is installed into the device since these actionscan significantly alter the remaining battery capacity.

The algorithm assumes that the battery capacity always decreases withlower temperature and always increases or stays the same with highertemperature. In this example, defibrillator 10 is in a stand-by orpower-down mode when it is not being used to treat a patient and is notrunning an automatic self-test. While in standby mode, defibrillator 10checks temperature via its temperature sensor 20 every two seconds. Whenthe defibrillator wakes up due to a temperature measurement at the highor low ends of its specified temperature range, the device will returnto stand-by mode without any further tests. At the low end, thedefibrillator will change the status indicator to indicate that thedevice is not ready to use.

If the present temperature is within the range of 0° C. to 50° C., thedefibrillator extracts only the most recent valid battery capacity testresult for each bin from the RTHL. If the present temperature bin (i.e.,the bin encompassing the present ambient temperature) has not beentested and it is lower than the lowest passing bin and higher than thehighest failing bin, the defibrillator runs its battery capacity test.Also, if the highest failing bin is higher than the lowest passing bin,the defibrillator runs its battery capacity test. Otherwise, thedefibrillator sets the present battery capacity to reflect the previoustest results from the RTHL without performing a battery capacity test:if the present bin is higher than a passing bin, the device indicates a"good battery" or non-warning status on its status indicator 22, and ifthe present bin is lower than a failing bin, the device indicates a "notgood battery" or warning status on its status indicator 22.

In the preferred embodiment, the device sets both high and low target(or "wake-up") temperatures before returning to stand-by mode after ause, a self-test, etc. The following table illustrates how the HI and LOregisters may be set:

    ______________________________________                                        Temp                                                                          Target                                                                        Registers                                                                             No Low Battery   Low Battery                                          ______________________________________                                        Instrument                                                                            HI = Bin 8 (disabled)                                                                          HI = Bin 8 (disabled)                                Temp in Bin                                                                           LO = Bin 7       LO = Bin 7                                           Instrument                                                                            if highest fail bin < lowest                                                                   if highest fail bin < lowest                         Temp in pass bin:        pass bin:                                            Bins 2-7                                                                              HI = Bin 8 (disabled)                                                                          HI = 1 Bin higher than                                       LO = MAX(1 Bin lower than                                                                      highest fail                                                 lowest pass, Bin 1)                                                                            LO = Bin 0 (disabled)                                        else:            else:                                                        HI = 1 Bin higher than                                                                         HI = 1 Bin higher than                                       present          present                                                      LO = 1 Bin lower than                                                                          LO = Bin 0 (disabled)                                        present                                                               Instrument                                                                            HI = Bin 2       if no postponed tests and                            Temp in Bin                                                                           LO = Bin 0 (disabled)                                                                          highest fail bin < lowest                            1                        pass bin:                                                                     HI = 1 Bin higher than                                                        highest fail                                                                  LO = Bin 0 (disabled)                                                         else                                                                          HI = Bin 2                                                                    LO = Bin 0 (disabled)                                Instrument                                                                            HI = Bin 1       HI = Bin 1                                           Temp in Bin                                                                           LO = Bin 0 (disabled)                                                                          LO = 0 (disable)                                     ______________________________________                                    

    ______________________________________                                        Target                                                                        Bin #       Target Temperature                                                ______________________________________                                        8            70 C. (disabled)                                                 7           56 C.                                                             6           25 C.                                                             5           15 C.                                                             4           10 C.                                                             3            5 C.                                                             2            0 C.                                                             1           -5 C.                                                             0           -55 C. (disabled)                                                 ______________________________________                                    

FIG. 5 is a block diagram showing an external defibrillator that may beused to implement the methods invention. Many of the elements shown inFIG. 5 bear no relation to this invention. They have been includedsolely to show one context in which the invention may operate.

As mentioned above, while defibrillators are particularly appropriatefor implementing this invention, the invention is not limited to use indefibrillators. In the defibrillator shown in FIG. 5, battery capacitytests are run daily as part of a suite of automatic self-tests, and theresults are recorded in the RTHL. The timing of the tests may be such,however, that hour-to-hour ambient temperature fluctuations are missed.This invention therefore provides a way to take current temperature intoaccount when providing a constant indication of device operationalstatus.

In defibrillator 100 of FIG. 5, the functions of the controller of theFIG. 1 defibrillator are distributed among an MPU 102 and two gatearrays 104 and 106. Gate array 106 also performs some of the functionsof the self-test initialization generator of FIG. 1.

Gate array 106 monitors temperature every 2 seconds in stand-by mode viaa temperature sensor 131 while the MPU and other parts of the device areinactive. In the embodiment shown in FIG. 5, temperature sensor is athermistor, such as model no. AL03006-535K-145-G1 from Keystone. If thecurrent temperature read by sensor 131 is equal to or warmer than a HItemperature target or equal to or colder than a LO temperature target(stored in registers in gate array 106), gate array 106 "awakens" therest of the device (i.e., changes the device from stand-by mode toself-test mode), and power is provided to MPU 102 and gate array 104. Atthat point, MPU 102 determines the reason it was awakened by reading anONOFF₋₋ REASON register within gate array 106.

If the reason was the reaching of a temperature target, MPU 102 looks toits own more accurate temperature sensor, A/D temperature sensor 109(such as an Analog Devices AD22100), to confirm the temperature. (Whilemore accurate than sensor 131, sensor 109 requires more power thansensor 131 and is therefore only used when the device has been taken outof stand-by mode, as opposed to every 2 seconds as with sensor 131.) MPU102 takes action appropriate to the new measured temperature, such as bylooking to an RTHL stored in Flash ROM 114 to determine and indicatedevice battery status and by setting new temperature targets, asdiscussed above.

Any battery capacity test or other self-test called for by the method ofthis invention is run by MPU 102. Gate array 106 operates the device'svisual status indicator 128 and beeper 119, which can function as anaudible status indicator.

One consequence of using two different temperature sensors is the needfor correlation between them. While the A/D temperature sensor 109 issufficiently linear over the useful range of temperatures that might beencountered by the device, temperature sensor 131 is non-linear above50° C. and below -10° C. A correction must be added to the sensor 131temperature readings in the non-linear range to compensate for thenon-linearity.

Modifications to the invention described above will be apparent to thoseskilled in the art. Such modifications are within the scope of thisinvention.

What is claimed is:
 1. A method of indicating operational status of anelectronic device, the method comprising the following steps:monitoringan environmental condition of the device; performing a plurality ofself-tests at a plurality of monitored environmental conditions, toobtain self-test results; determining from results of the performingstep whether the device operational status is acceptable or unacceptableat each monitored environmental condition; storing an association ofself-test results and environmental conditions at which the self-testswere performed; indicating operational status of the electronic devicefor a partially monitored environmental condition based on the storedself-test results, wherein the plurality of self-tests comprise one ormore different tests.
 2. The method of claim 1 wherein the storing stepcomprises storing a maximum number of self-test results.
 3. The methodof claim 1 wherein the environmental condition is temperature.
 4. Themethod of claim 3 wherein the device is a battery-operated device andthe self-test is a battery capacity test.
 5. The method of claim 4further comprising:if a battery capacity test has not been performedwithin a target temperature, and if the target temperature is lower thana temperature of a lowest acceptable battery capacity test result andhigher than a temperature of a highest unacceptable battery capacitytest result; then performing a battery capacity test; storing anassociation of a battery capacity test result from the previous step sand the target temperature; indicating the device operational statusfrom the results from the battery capacity test stored in the previousstep, and setting a new target temperature.
 6. The method of claim 5further comprising:if a target temperature of an unacceptable batterycapacity test result is higher than a target temperature of anunacceptable battery capacity test resul, then; performing a batterycapacity test; storing an association of a result from the batterycapacity test from the previous step and a current target temperature;and indicating an operational status of the device based on the resultfrom the battery capacity test stored in the previous test.
 7. Themethod of claim 4 wherein the battery-operated device is an externaldefibrillator.
 8. A method of indicating operational status of anelectronic device, the method comprising the following steps:monitoringan environmental condition of the device; performing a self-test at themonitored environmental condition; determining a self-test result fromthe self-test, the self-test result being a device operational status ofacceptable or unacceptable; and storing an association of the self-testresult and environmental condition at which the self-test was performed;repeating the above steps at a plurality of different monitoredenvironmental conditions; and indicating operational status of theelectronic device based on the stored self-test result at a presentlymonitored environmental condition.
 9. The method of claim 8 wherein thestoring step comprises storing a maximum number of self-tests results.10. The method of claim 8 wherein the environmental condition istemperature.
 11. The method of claim 10 wherein the device is abattery-operated device and the self-test is a battery capacity test.12. The method of claim 11 further comprising:if a battery capacity testhas not been performed within a target temperature, and if the targettemperature is lower than a temperature of a lowest acceptable batterycapacity test result and higher than a temperature of a highestunacceptable battery capacity test result; then performing a batterycapacity test; storing an association of a battery capacity test resultfrom the previous step and the target temperature; indicating the deviceoperational status from the results from the battery capacity teststored in the previous step; and setting a new target temperature. 13.The method of claim 12 further comprising:if a target temperature of anunacceptable battery capacity test result is higher than a targettemperature of an unacceptable battery capacity test result, then:performing a battery capacity test; storing an association of a resultfrom the battery capacity test from the previous step and a currenttarget temperature; and indicating an operational status of the devicebased on the result from the battery capacity test stored in theprevious test.
 14. The method of claim 11 wherein the battery-operateddevice is an external defibrillator.